Valorizing recycled paper sludge by a bioethanol production process with cellulase recycling

Abstract

The feasibility of cellulase recycling in the scope of bioethanol production from recycled paper sludge (RPS), an inexpensive byproduct with around 39% of carbohydrates, is analyzed. RPS was easily converted and fermented by enzymes and cells, respectively. Final enzyme partition between solid and liquid phases was investigated, the solid-bound enzymes being efficiently recovered by alkaline washing. RPS hydrolysis and fermentation was conducted over four rounds, recycling the cellulases present in both fractions. A great overall enzyme stability was observed: 71, 64 and 100% of the initial Cel7A, Cel7B and β-glucosidase activities, respectively, were recovered. Even with only 30% of fresh enzymes added on the subsequent rounds, solid conversions of 92, 83 and 71% were achieved for the round 2, 3 and 4, respectively. This strategy enabled an enzyme saving around 53-60%, while can equally contribute to a 40% reduction in RPS disposal costs.

Insights into the economic viability of cellulases recycling on bioethanol production from recycled paper sludge

“…1A). An extended description of this process has been reported by Gomes et al (2016Gomes et al ( , 2018.…”

“…Considering the results and specifications described by Gomes et al (2016Gomes et al ( , 2018, a cellulases recycling scenario was envisioned assuming the recovery of both liquid and solid fractions, with only 50% of fresh enzyme being utilized on each recycling stage (Rec2Frac). As expected, there was a clear reduction in the total cost of enzyme -38%and consequently the corresponding contribution to the total costs D.G.…”

“…Nevertheless, this material also contains a considerable amount of sugars that can be valorized through multiple products, namely bioethanol. In fact, several studies have already demonstrated the practical feasibility of RPS for the production of bioethanol (Marques et al, 2008a;Gomes et al, 2016Gomes et al, , 2018 or lactic acid (Marques et al, 2008b). Chen et al (2014) have recently demonstrated that from an economic point of view, the conversion of different paper manufacturing residues is in fact viable to implement on an industrial scale.…”

“…The economics of RPS conversion was first analyzed considering no enzyme recycling, which represents the first study of this kind for this particular material. Afterwards, based on experimental data gathered in previous research (Gomes et al, 2016, the impact of cellulase recycling was assessed. Finally, a sensitivity analysis demonstrated the effect of different variables on the process economics and the validity of the main findings of this work.…”

Optimization of bacterial nanocellulose fermentation using recycled paper sludge and development of novel composites

“…Alternatives to treat paper sludge are being studied. Marques et al 2008a, b, 2009and Gomes et al 2016 exploited the high lignocellulosic content sludge material as carbon source to produce lactic acid and bioethanol (Marques et al 2008a(Marques et al , b, 2009Prasetyo and Park 2013;Gomes et al 2016). Bacterial nanocellulose (BNC), a Biotech nanocellulose, features high porosity, high crystallinity, high degree of polymerization, high mechanical strength in wet state, high water holding capacity, low density, biocompatibility, non-toxicity and biodegradability.…”